This invention relates to mine roof supports, and in particular to a mine roof support unit for a walking frame roof support assembly, the unit having a two-part goaf shield fitted between its roof cap and its floor sill.
Roof support units having two-part goaf shields are known, the two parts of such shields being hinged together in such a manner that the hinge moves towards the goaf side of a mine working as the roof support props of the unit are retracted. Thus, DT-OS No. 2,448,367 and U.S. Pat. No. 3,483,705 each discloses a roof support unit of this type, the goaf shield being pivotably mounted on the roof cap by means of pin-and-slot connections. This permits the roof cap to tilt slightly so as to accommodate variations in the roof of the working.
DT-OS No. 1,237,308 also discloses a roof support unit having a two-part hinged goaf shield. The two goaf shield parts are hinged respectively to the roof cap and the floor sill of the unit so that, as the roof support props are retracted, the hinge between the two goaf shield parts moves towards the goaf side of the working. DT-AS No. 2,403,834 discloses a two-part goaf shield which is connected to the roof cap by means of a universal joint which permits the roof cap to tilt to accommodate roof unevenness without deformation forces acting on the goaf shield. The universal joint also has the effect of limiting the tilting movement of the cap about its longitudinal axis, so that excessive tilting of the cap, in the unloaded condition, is prevented.
The disadvantage of all these known arrangements is that the load acting on the goaf shield, owing to the presence of rock and rubble in the goaf side of the working, may hinder or even prevent the hinge connection between the two parts of the shield moving, and hence lowering of the roof cap and advance of the unit may be prevented.
The main object of the invention is to provide a mine roof support unit of the initially stated type, whose goaf shield is such that the roof cap can be lowered sufficiently to permit advance of the unit, without the hinge connection between the two shield parts moving towards the goaf side of the working.
Another object of the invention is to ensure, as far as is possible, considerable relative mobility between the roof cap and the goaf shield, and to prevent forces, which otherwise severely limit the mobility of the cap and its ability to adapt to any unevenness of the roof, from being transmitted to the shield by way of the cap.
Yet another object is to provide an advantageous arrangement for shielding the sides of the roof support unit.